This invention relates to adsorbents and more particularly it relates to improved alumina based bodies suitable for use as adsorbents and the method of making the bodies.
In forming alumina bodies suitable for adsorbing HCl, H.sub.2 O, CO.sub.2 or H.sub.2 S, or the like, the bodies can be formed by several methods. For example, activated alumina powder can be mixed with water to make a slurry which is extruded to form pellets. Or, dry activated alumina powder can be added at a steady rate to a rotating pan and an aqueous solution sprayed on the powder as the pan rotates. The rotating pan forms the powder into spheres as it is sprayed. In another method, spheres or rounded bodies can be made from a viscous slurry of the activated alumina and aqueous solution using the so-called "oil drop" method.
It has been discovered that activated alumina impregnated with sodium containing compounds, for example sodium oxide, provides for increased adsorption. For example, U.S. Pat. No. 5,316,998 discloses an HCl adsorbent, and method of making and using the adsorbent, the adsorbent comprising an activated alumina promoted with an alkali metal oxide. The adsorbent contains at least about 5% alkali metal oxide. This patent discloses adding the alkali metal oxide using an alkali metal salt of an organic compound that decomposes at temperatures below 500.degree. C. and liberates the organic portion.
U.S. Pat. No. 5,505,926 discloses an HCl adsorbent and method of making and using the adsorbent, the adsorbent comprising an activated alumina promoted with an alkali metal in an amount such that if calculated as alkali metal oxide, the adsorbent contains at least about 5% by weight alkali metal oxide. The adsorbent is used for removal of HCl from a fluid stream.
U.S. Pat. No. 4,755,499 discloses a sorbents comprising (a) an alumina substrate having a pore volume between 0.4 and 0.8 cc/g, and (b) an alkali or alkaline earth component, for example, sodium carbonate, wherein the amount of the alkali or alkaline earth component is between 50 and 400 .mu.g per m.sup.2 of the substrate. The sorbents of the invention are effective for the removal of nitrogen oxides, sulfur oxides and hydrogen sulfide from waste gas streams.
U.S. Pat. No. 2,378,155 discloses a process of producing adsorbent alumina comprising drying aluminum hydroxide to a water content of between 2-15 per cent by weight, and subsequently heating the resulting alumina in contact with water under super-atmospheric pressure at a temperature above 100.degree. C.
U.S. Pat. No. 4,855,276 discloses an adsorbent composition, method of preparing same, and method of treating a fluid stream with the adsorbent. Alumina and carbon are combined with water in preferred proportions in one embodiment. Sodium bicarbonate and impregnates such as Group 1A metal hydroxides and Group 7A salts of Group 1A metals can be added. Improved efficiency of removal of compounds such as hydrogen sulfide is achieved, and ignition temperature is reduced.
U.S. Pat. No. 5,096,871 discloses alumina-containing acid adsorbents and process for producing same. The adsorbents comprise activated alumina and an amorphous alkali (preferably sodium) aluminum silicate. The ratio of Si:Al in the amorphous material is preferably 0.25-100:1 by weight. A process for producing such adsorbents comprises treating activated alumina with a solution of an alkali metal silicate followed by an alkali metal aluminate, and forming agglomerates of the treated alumina at a temperature below about 90.degree. C., aging the agglomerates at a temperature in the range of 20.degree.-90.degree. C., and calcining the aged agglomerates at a temperature in the range of 200.degree.-500.degree. C.
However, in spite of these disclosures, there is still a great need for improved alumina bodies containing at least two alkali or alkaline earth metals, alkali or alkaline earth metal compounds or combinations thereof.